In many optical local area networks (LANs) and optical backplanes having a bus-type architecture, an optical repeater receives and combines optical signals from optical transmitters in system nodes, amplifies, and individually retransmits back to optical receivers in the system nodes. One of the major problems is that an optical receiver in the optical repeater has difficulty in accurately receiving digital information from multiple transmitters which are transmitting at different optical power output levels. The optical power levels received from typical optical transmitters may differ by a few dB in optical level. The difference in optical power levels received at the optical repeater is different not only because the light emitting diodes (LEDs) or lasers, which are used as light sources differ in their outputs, but also because these light sources are connected to the optical repeater via connectors, optical couplers, and interconnecting optical fibers which can introduce optical power losses.
The problem created by received signals having varying optical power levels is the difficulty of distinguishing by the optical receiver between logical "1's" or "0's" from the various optical transmitters. Optical receivers are of two types: dc coupled and ac coupled. If a receiver is of the dc coupled type, it is very difficult to find a common threshold which allows adequate noise margins for different levels of transmitted signals. If the receiver is of the ac coupled type using edge differentiation, adjacent bits corresponding to the "1" state from different transmitters can cause a problem. If two adjacent bits are both a "1" logic signal but at two different optical power levels, there is a significant "edge" or transition in amplitude between the two adjacent "1" logic levels; and the receiver's edge detection mechanism incorrectly interprets that as a transition between logical values.